1. Field of the Invention
The present invention relates to a gas insulated switchgear, and particularly, to a switching mechanism of a circuit breaker for a gas insulated switchgear.
2. Description of the Background Art
A high voltage gas insulated switchgear having tens of kV or hundreds of kV rate voltage related to the present invention generally includes a circuit breaker, a current transformer, a disconnecting switch for load line, a disconnecting switch for power source line and a bushing for electrical insulation. The gas insulated switchgear is installed on an electrical power supplying line and is used when a circuit is opened/closed for testing electrical equipment or the electrical power supplying line in a normal usage status. Also, the gas insulated switchgear breaks the circuit between electric source and load when abnormal current due to ground faults or short circuit, etc., is generated in order to protect electrical power supplying system and electrical load apparatuses safely.
Presently, in most countries, in order to operate the electric power supplying system, a six Fluoric Sulfur (abbreviated as SF6) gas insulated switchgear or a switchgear called as an SF6 gas ring main unit is installed on the ground or underground as a branching apparatus and a dividing apparatus of the lines.
One of the principal functions of the high voltage switchgear using the SF6 gas as the insulating material is a function of extinguishing rapidly an arc generated when the circuit is opened or closed.
There are arc extinguishing methods used recently such as an electromagnetic arc rotating type, a thermal expansion type, an arc dividing grid type and a puffer type, etc.
The puffer type can be divided into a straight moving type and a rotating type, and the present invention relates to the straight moving type arc extinguishing method.
As a reference, arc discharging means a status that some of electrode material is evaporated to become gas, and can be referred as gas discharging. In addition, since the electricity is somewhat remained on the end of a moving arc contactor and a fixed arc contactor right after the flowing of electricity is blocked and generates arc discharging to interrupt the electric current blocking, the arc generated when the circuit is closed, that is, tripped in the gas insulated switchgear should be extinguished effectively and rapidly to protect the lines and the load apparatuses safely.
FIG. 1 is a brief view showing an outer appearance of a conventional gas insulated switchgear, FIG. 2 is a cross-sectional view showing inside of a circuit breaker in the conventional gas insulated switchgear, FIG. 3 is a cross-sectional view showing a switching mechanism which is a principal part of the breaker in the conventional gas insulated switchgear, showing the closed circuit, that is, the status of circuit connection, and FIG. 4 is a cross-sectional view showing the switching mechanism which is a principal part of the breaker in the conventional gas insulated switchgear, showing opened circuit, that is, the status of circuit breaking.
As shown in FIG. 1, the gas insulated switchgear 1 comprises: a breaker 10 for breaking a circuit; a current transformer 20 for detecting amount of current flowing on the circuit; a disconnecting switch 30 for load line for breaking connection to load side; a disconnecting switch 40 for power source line for breaking connection to power source side; and a bushing 50 for insulating an electric terminal.
As shown in FIG. 2, the breaker 10 of the gas insulated switchgear 1 comprises: conductors C1 and C2 connected to power source side or to the load side; and a switching mechanism connected to the conductors C1 and C2 to connect or break the circuit, and the switching mechanism can be divided into a fixed portion 10A and a movable portion 10B.
As shown in FIGS. 3 and 4, the switching mechanism which is a principal part of the circuit breaker 10 for the gas insulated switchgear 1 is divided into the fixed portion 10A and the movable portion 10B, and the fixed portion 10A comprises a fixed contactor 11 and a fixed arc contactor 12 located in the fixed contactor 11.
In addition, the movable portion 10B comprises: a main cylinder 13; a movable cylinder 14 movably installed on an inner upper part of the main cylinder 13, the movable cylinder 14 including SF6 gas therein; a cylinder rod 15 located in a compressing chamber 14a of the movable cylinder 14 and movable with the movable cylinder 14; a sealing member 16 fixedly installed in the movable cylinder 14 so that an outer circumferential surface of the cylinder rod 15 is abutted thereon for sealing the compressing chamber 14a; a connecting rod 17 installed to be connected to a lower part of the cylinder rod 15, and connected to an actuator device (not shown) such as a hydraulic system in order to supply power to the switching mechanism according to a command signal of circuit breaking; a movable arc contactor 18 installed on the upper part of the cylinder rod 15 and selectively connected/separated to/from the fixed arc contactor 11; and a nozzle 19 installed on an upper part of the movable cylinder 14. The movable cylinder 14 and the cylinder rod 15 are connected to each other by a connecting member such as a ring member for connecting (not shown), and therefore, these can move together.
In addition, the conductors C1 and C2 for connecting circuit with the power source or with the load are connected to the fixed contactor 11 of the fixed portion 10A and to the main cylinder 13 of the movable portion 10B respectively, as shown in FIG. 2.
In a normal status that the normal current flows in the circuit between the power source and the load, the movable arc contactor 18 is contacted to the fixed arc contactor 12 to maintain the closed circuit status as shown in FIG. 3, and the conductors C1 and C2 are connected electrically.
On the other hand, when abnormal large current flows due to ground fault or short circuit generated in the circuit between the power source line and the load line, a controller (not shown) recognizes it and outputs a command signal of circuit breaking, and accordingly, the actuator device (not shown) pulls the connecting rod 17 in the arrow direction and the cylinder rod 15 connected to the connecting rod 17 is also moved in the arrow direction. At that time, the movable arc contactor 18 located on the upper part of the cylinder rod 15 and the movable cylinder 14 connected to the cylinder rod 15 are also moved in the arrow direction.
The compressing chamber 14a is moved downward together with the cylinder rod 15, and at that time, since the sealing member 16 is fixed, volume of the compressing chamber 14a is reduced rapidly and the movable arc contactor 18 is separated from the fixed arc contactor 12 simultaneously.
As described above, at the moment that the movable arc contactor 18 is separated from the fixed arc contactor 12, the SF6 gas in the compressing chamber 14a is injected through the nozzle 19 by the pressure to extinguish the arc. However, since the arc generated at the moment that the movable arc contactor 18 is separated from the fixed arc contactor 19, is the gas of high temperature and high pressure, the pressure of the arc is higher than that of the SF6 gas injected through the nozzle 19, and therefore, the injection of SF6 gas is not made effectively. In addition, when the arc gas is expanded, there is a limit of space to accept the gas, and therefore it is difficult to extinguish the arc rapidly.
Therefore, the function of extinguishing the arc by injecting a large amount of the SF6 gas in the compressing chamber 14a rapidly, that is, the arc extinguishing speed is an important function of the gas insulated switchgear, and a lot of researches are being proceeded.
A method for increasing SF6 gas injecting pressure by increasing the gas pressure in the compressing chamber had been suggested as a conventional method for improving arc extinguishing speed, however, in above method, required output of the actuator device pulling the connecting rod should be increased in proportion to the gas pressure, and also, stroke between compressed status and expanded status of the compressing chamber should be increased, and therefore, the sizes of the breaker and the gas insulated switchgear are increased and the fabrication cost is increased consequently.
Therefore, an object of the present invention is to provide a switching mechanism of a circuit breaker for a gas insulated switchgear which is able to improve arc extinguishing function by providing a compressing chamber as a space for expanding arc gas without increasing a stroke between compressed status and expanded status of the compressing chamber when the switching mechanism is operated to circuit breaking position, that is, in trip operation.
Another object of the present invention is to provide a switching mechanism of a circuit breaker for a gas insulated switchgear which is able to improve extinguishing function by compressing a compressing chamber to inject a large amount of insulating gas rapidly when the breaker is tripped.
To achieve the objects of the present invention, as embodied and broadly described herein, there is provided a switching mechanism of a circuit breaker for a gas insulated switchgear comprising: a fixed arc contactor electrically connected to a power source or to a load; a main cylinder fixedly installed to face the fixed arc contactor in a vertical direction; a movable cylinder movably installed on an upper part of the main cylinder, the movable cylinder having a compressing chamber including insulating gas; a cylinder rod extending from a predetermined position of lower part of the main cylinder to the inside of the movable cylinder, and being connected to the movable cylinder and movable with the movable cylinder; a movable arc contactor installed on an upper part of the cylinder rod and contacted/separated selectively to/from the fixed arc contactor depending on vertical movement of the cylinder rod; a nozzle installed on an upper part of the movable cylinder for injecting the insulating gas in the compressing chamber; and a movable sealing means installed between the movable cylinder and the cylinder rod, and movable in a vertical direction in order to provide the compressing chamber of which volume can be varied.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.